Device for controlling an internal combustion engine with controlled ignition and direct injection

ABSTRACT

A device for controlling a controlled-ignition direct-injection internal combustion engine to avoid abrupt variations in torque when switching from homogeneous-charge to stratified-charge combustion mode and vice versa, includes a determinator for determining a reference value of a transmission torque as a function of a position of an accelerator pedal. A calculator is provided for calculating a value of at least one command of at least one controller for controlling the engine based on a datum value for a transmission torque. A corrector is configured to correct the datum value of the transmission torque as a function of the engine combustion mode by applying a torque correction taken from a correction table as a function of at least one variable representing a load on the engine. The calculator has a first inverse model of the engine in its homogeneous-charge combustion mode and a second inverse model of the engine in its stratified-charge combustion mode.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a device for controlling acontrolled-ignition direct-injection internal combustion engine,particularly a high-pressure, direct-injection engine.

According to document DE 42 32 974, a control device for acontrolled-ignition internal combustion engine has a device fordetermining a datum torque. It also comprises a device for determiningthe throttle valve angle which determines this angle as a function ofthe datum torque. For this purpose, in the device for determining thethrottle valve angle, there is an inverse model of the filling of theinlet tract and of the cylinder of the internal combustion engine and atable of throttle valve opening angles.

In publication SAE 960465 "Gasoline direct injection: Actual trends andfuture strategies for injection and combustion systems", by G. K.Fraidl, W. F. Piock and M. Wirth, it is proposed that a direct-injectioncontrolled-ignition internal combustion engine be made to run instratified-charge combustion mode in the lower part load spectrum. Forthis purpose, an air/fuel ratio greater than 100 is preferably set. Inthe upper part-load spectrum, it is proposed that the engine be run inhomogeneous-charge or in stratified-charge combustion mode, alternately.Thus, a system for the subsequent treatment of the exhaust gases, suchas a DeNox catalyst, can be regenerated. In this way, the legallyimposed restrictions on emission can be met.

SUMMARY OF THE INVENTION

However, an abrupt variation of the torque on the output shaft of theinternal combustion engine may occur during the change fromhomogeneous-charge combustion mode to stratified-charge combustion modeand vice versa, and this is to the detriment of driving comfort.

The object of the invention is to produce a control device designed tominimize this variation in torque when changing from homogeneous-chargeto stratified-charge combustion mode and vice versa.

This object is achieved by means of a device for controlling acontrolled-ignition direct-injection internal combustion engine,comprising means of determining a reference value of a transmissiontorque as a function of the position of an accelerator pedal, means ofcalculating the value of at least one command of at least one means ofcontrolling the engine on the basis of the datum value for thetransmission torque, said calculation means comprising a first inversemodel of the engine in its homogeneous-charge combustion mode and asecond inverse model of the engine in its stratified-charge combustionmode, and correction means designed to correct the datum value of thetransmission torque as a function of the engine combustion mode byapplying a torque correction taken from a correction table as a functionof at least one variable representing the load on the engine.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In a preferred embodiment of the invention, the control device has anadaptation device which adapts the torque correction values in thecorrection table as a function of an internal combustion engine outputvariable. Thus, the modifications to the effective behavior of theengine which are brought about by manufacturing tolerances or by theaging of the engine, can be compensated for.

In another advantageous embodiment of the invention, the adaptation isperformed within a predetermined period of time around a change incombustion mode from homogeneous-charge to stratified-charge or fromstratified-charge to homogeneous-charge.

Other features and advantages of the control device according to theinvention will become clear from reading the description which willfollow and from examining the appended drawings, in which:

FIG. 1 depicts a control device for an internal combustion engineaccording to the invention, and

FIG. 2 depicts a second embodiment or the control device according tothe invention.

Elements of identical construction or which have the same function aredenoted by the same reference on all the drawings.

FIG. 1 shows a control device according to the invention which comprisesmeans 0 of determining a datum value TQE₋₋ SP for a transmission torque.A sensor 10 for sensing the position of an accelerator pedal 11 whichmeasures the position PV of the accelerator pedal is connected to thedetermining means 0. The means 0 of determining the datum value of thetransmission torque comprise a table in which the datum values for thetransmission torque are recorded as a function at least of the positionof the accelerator pedal. The transmission torque datum values can thusbe stored in memory in the table as a function of other operatingparameters such as, for example, the rotational speed N of the engineand/or the coolant temperature. It is also possible to anticipatecorrecting the transmission torque datum value as a function ofadditional loads, such as, for example, an alternator or anair-conditioning unit.

The datum value TQE₋₋ SP for the transmission torque is, corrected in afirst summer S1 with a torque correction TQE₋₋ COR which is describedlater. The datum value TQE₋₋ SP for the transmission torque istransmitted to calculation means 2 which comprise a first inverse model21 and a second inverse model 22 of the internal combustion engine. Suchan inverse model preferably comprises a model of the filling of theinlet tract as described, for example, in document WO 96/32579, thecontent of which is also included here by reference. Furthermore, suchan inverse model comprises a model of the combustion in the cylinders ofthe internal combustion engine. Using these first and second inversemodels 21, 22, the datum values TQE₋₋ SP of the transmission torque canbe associated with various commands for control means of a control unit40 which takes account of the dynamics of the internal combustion engineinlet circuit. The values of the control commands are defined by enginetest bed measurements.

The control unit 40 comprises control means, namely a throttle valve401, at least one injector 402 and an ignition device 403. The controlunit 40 may possibly comprise other control means such as automaticcontrol of valve lift or an acoustic tuning device which varies theeffective length of the inlet manifold. The control means act on theinternal combustion engine 41 and control the torque it delivers. Thesecontrol means may thus, by way of example, be effected by interruptingthe injection during a changeover from stratified-charge combustion modeto homogeneous-charge combustion mode. These interruptions may beperformed on one or more cylinders at a time during the period of timein which the flow of air entering the cylinder is greater than thedesired air flow.

The control device is intended for an internal combustion engine 41 withhigh-pressure direct injection and controlled ignition. Into eachcylinder of this type of internal combustion engine 41 there opens aninjector 402 and a spark plug which forms part of the ignition device403. It is thus possible, in an internal combustion engine of this type,to achieve either a homogeneous-charge combustion mode, that is to say amode in which there is a uniform distribution of the fuel through thecombustion chamber, or a stratified-charge combustion mode, that is tosay a mode where there is only a localized high concentration of fuel,preferably near to the spark plug.

When the engine is operating at part load, the use of astratified-charge combustion mode makes it possible to reduce the fuelconsumption by what may be as much as 30% by comparison with an enginewith indirect injection into the inlet tract operating inhomogeneous-charge mode. This is because the throttle valve 401 isalmost completely open and because of the reduction in associatedpumping losses. Furthermore, reliable combustion is possible instratified-charge operation even for small quantities of fuel when thefuel is locally stratified around the spark plug. The stratified chargeis obtained by injecting very late in the compression stroke of thecylinder concerned. For operation with a stratified charge, the torquesupplied by the internal combustion engine is controlled by controllingthe mass of fuel injected during each cycle of the cylinder concerned.

In homogeneous-charge mode, the torque of the internal combustion engineis controlled by the mass of air let into the cylinder on each cycle. Inhomogeneous-charge operation, it is possible to have a maximum value ofthe excess air coefficient 1=1.5 for reliable combustion. For values1>1.5, reliable combustion is no longer guaranteed.

Limitations such as problems with preparing the charge, driving comfort,and pollutant emissions governed by regulations prevent an internalcombustion engine from being run with a stratified charge under all loadconditions. As a result, at light and medium load, the internalcombustion engine is operated in stratified-charge mode, whereas at highload and full load, it is operated with a homogeneous charge.Furthermore, the engine may possibly operate, temporarily alternatingbetween stratified-charge and homogeneous-charge mode at light andmedium load, to allow the regeneration of a catalytic converter in whichthe oxides of nitrogen are stored.

The change of combustion mode, from homogeneous charge to stratifiedcharge and vice versa is controlled by a controller 3. The controller 3determines whether the internal combustion engine needs to operate instratified-charge mode or in homogeneous-charge mode, as a function ofthe load or the degree of saturation of the catalytic converter in whichthe oxides of nitrogen are stored.

The first inverse model 21 of the internal combustion engine representsthe behavior of the internal combustion engine for operation with ahomogeneous charge, whereas the second inverse model 22 represents thebehavior of the internal combustion engine for operation with astratified charge.

The controller 3 controls a first switch 23 so that the datum valueTQE₋₋ SP of the transmission torque is transmitted to the first inversemodel 21 when operating with a homogeneous charge, or to the secondinverse model 22 when operating with a stratified charge. Likewise, thecontroller 3 controls a second switch 24 so that the output values fromthe first inverse model 21 are transmitted to the control means 40 whenoperating in homogeneous-charge mode, or so that the output values fromthe second inverse model 22 are transmitted to the means 40 whenoperating in stratified-charge mode.

The first and second inverse models 21, 22 calculate at least onecontrol value for at least one control means. The datum value TQE₋₋ SPfor the transmission torque is transmitted to the appropriate inversemodel 21, 22.

The control device also comprises correction means 5 which correct thedatum value TQE₋₋ SP of the transmission torque. The correction means 5comprise a correction table 51 in which torque corrections TQE₋₋ COR arewritten as a function of at least one variable representing the engineload. The torque correction values TQE₋₋ COR are calculated frommeasurements made on engine test bed as a function of the values ofvariables representing the load on the engine. These variablesrepresenting the load on the engine may be the inlet pressure, a mass ofair per inlet stroke of the cylinder, the rotational speed N and theextent to which the throttle valve 401 is open, an injection period oralternatively, a combination of these variables. By way of example, itis possible to use two-dimensional tables which can be addressed as afunction of the inlet pressure and of the engine speed.

The correction means 5 also comprise a switch 52 which, in operationwith stratified charge, connects the output of the correction table 51to the first summer S1. In operation with homogeneous charge, the switch52 is open. This is why the transmission torque datum value TQE₋₋ SP isnot corrected with the engine torque correction value TQE₋₋ COR. As analternative to the switch 52, it is also possible to provide a switchingdevice which supplies the first summer S1 with an algebraic value of thetorque correction TQE₋₋ COR, the sign of which is a function of theengine combustion mode.

Advantageously, the control device also comprises adaptation means 6which comprise a delay element (not depicted) to which an outputvariable of the internal combustion engine 41 is transmitted. Thedifference between the current value of the output variable and thevalue supplied by the delay element is formed in the adaptation means 6,and integrating this difference provides an adaptation value with which,at a predetermined instant, for example after the change fromhomogeneous-charge combustion mode to stratified-charge combustion modeor vice versa, the torque correction value TQE₋₋ COR associated with thecurrent value of the variable representing the load on the engine isadapted.

It is advantageous for the adaptation value to be calculated in apredetermined period of time around a change in combustion mode fromhomogeneous charge to stratified charge or around a change in combustionmode from stratified charge to homogeneous charge. In particular, atsteady-state part load, when changing from homogeneous-charge combustionmode to stratified-charge combustion mode and vice versa, performed witha view to regenerating the catalyst, the output variable is a directmeasure of the quality of the torque correction. By thus calculating,during this predetermined period of time, a value for adapting thetorque correction for the corresponding load operating point of theinternal combustion engine, variations due to the aging of the internalcombustion engine and the production spread are taken into account. Aswitch 6a, which is closed during the adapting of a torque correctionvalue TQE₋₋ COR, and which is open at other times, is associated withthe adaptation means 6.

FIG. 2 shows a second exemplary embodiment of the control deviceaccording to the invention. The calculation means 2 comprise a regulator25, the input variable of which is the difference, calculated by thesummer S2, between the datum value TQE₋₋ SP and an estimated value TQE₋₋EST of the transmission torque. The calculating of the estimated valueTQE₋₋ EST of the transmission torque is described later. The regulator25 may be a proportional, integral and derivative regulator, but mayalso be a regulator of some other type, for example a non linearregulator.

In a third summer S3, the output signal from the regulator 25 is addedto the datum value TQE₋₋ SP of the transmission torque and supplied tothe first inverse model 21 or to the second inverse model 22, dependingon the position of the first switch 23. Depending on the position of thefirst and of the second switches 23, 24, it is either the first inversemodel 21 or the second inverse model 22 which calculates the commandsfor the control means of the control unit 40.

The commands for the control means are transmitted to an observer 7.Alternatively, measured values of the controls performed, obtained forexample by a position sensor on the throttle valve 401, are transmittedto the observer. The observer 7 has a first model 71 and a second model72 of the internal combustion engine. The first and second models 71, 72are respectively the inverse of the first and second inverse models 21,22. The first model 71 and the second model 72 respectively calculate anobserved value TQE₋₋ MOD of the transmission torque. The command controlvalues are thus converted into an observed value TQE₋₋ MOD of thetransmission torque by the first model 71, when combustion is inhomogeneous-charge mode, or by the second model 72, when combustion isin stratified-charge mode. As seen earlier in conjunction with theinverse models 21 and 22, switches, not depicted, are provided on theinput and output of the first and second models 71, 72 and activate thefirst and second models 71, 72 as a function of the command signals fromthe controller 3.

The torque correction TQE₋₋ COR originating from the correction means 5and an estimated value TQFRU₋₋ EST of an additional resistive torquesuch as, for example, the resistive torque generated by a variation inthe profile of the road or by the wind are subtracted from the observedtransmission torque value TQE₋₋ MOD in a summer S4. An observed valueDTQ₋₋ MOD of a torque available for acceleration is therefore obtainedat the output of the summer S4. The observed value DTQ₋₋ MOD of thetorque available for acceleration is integrated in an integrator 73 anddivided by a predetermined value J of a moment of inertia of thevehicle. The predetermined value J of the moment of inertia is stored ina memory or may be calculated as a function of signals from sensors thatsense the occupancy of the seats or the presence of a trailer. Theoutput variable from the integrator is the observed rotational speed N₋₋MOD.

A sensor 411 that senses the rotational speed measuring the rotationalspeed N of a crankshaft of the internal combustion engine 41 isassociated with the control device according to the invention. Therotational speed N represents the output variable of the internalcombustion engine 41. The internal combustion engine output variable, inanother embodiment of the control device, may also be a pressure in thecombustion chamber or a torque measured on the output shaft of theinternal combustion engine.

In a fifth summer S5, the difference between the observed rotationalspeed N₋₋ MOD and the rotational speed N is formed and transmitted tothe adaptation means 6. This difference is integrated by the adaptationmeans 6, preferably during the predetermined period of time around achange in combustion mode from homogeneous charge to stratified chargeor vice versa. At the end of the predetermined period of time, the sumof the integral at the output of the adaptation means 6 and the valueTQE₋₋ COR of the torque correction for the actual current loadconditions is stored in memory as a new torque correction value TQE₋₋COR in the correction table 51. For this purpose, there is a switch 6awhich, depending on its position, which is controlled by the controller3, connects or does not connect the adaptation means 6 to the correctionmeans 5.

The difference between the observed rotational speed N₋₋ MOD and therotational speed N is also transmitted to first estimating means 8which, outside of the predetermined period of time, calculate anestimated value TQFRU₋₋ EST of an additional resistive torque from aproportional, integral and derivative fraction of the input variable.The estimated value of the additional resistive torque TQFRU₋₋ ESTrepresents, as was seen earlier, an estimate of the losses due, forexample, to atmospheric friction or to an error when modeling the lossesof the internal combustion engine. The estimated value TQFRU₋₋ EST mustpreferably remain constant during the predetermined period of time.

Second estimating means 9 calculate an estimated value TQE₋₋ EST of thetransmission torque as a function of the rotational speed N and of theestimated value TQFRU₋₋ EST of the additional resistive torque. Thesecond estimating means 9 comprise a differentiator which calculates thederivative of the rotational speed N and therefore an estimated value ofthe acceleration of the vehicle. This estimated value of theacceleration is then multiplied by the predetermined value J of themoment of inertia of the vehicle thus giving an estimated value for anacceleration torque which is added to the estimated value TQFRU₋₋ EST ofthe additional resistive torque in order to obtain an estimated valueTQE₋₋ EST of the transmission torque.

What is claimed is:
 1. A device for controlling a controlled-ignitiondirect-injection internal combustion engine, comprising:a determinatorfor determining a reference value of a transmission torque as a functionof a position of an accelerator pedal; a calculator for calculating avalue of at least one command of at least one controller for controllingthe engine based on a datum value for a transmission torque, saidcalculator having:a first inverse model of the engine in ahomogeneous-charge combustion mode; and a second inverse model of theengine in a stratified-charge combustion mode; and a correctorconfigured to correct the datum value of the transmission torque as afunction of the engine combustion mode by applying a torque correctiontaken from a correction table as a function of at least one variablerepresenting a load on the engine.
 2. The control device according toclaim 1, including an adaptor for adapting the torque corrections in thecorrection table as a function of an engine output variable.
 3. Thecontrol device according to claim 2, wherein the adapting is performedin a predetermined period of time around a change in combustion modefrom homogeneous charge to stratified charge and vice versa.
 4. Thecontrol device according to claim 3, including an observer to supply anobserved value of the engine output variable as a function of at leastone command for controlling the engine, said adaptor performing theadaptation as a function of a combination of an observed value and of ameasured value of the output variable.
 5. The control device accordingto claim 4, including an estimator which, outside a predetermined periodof time around a change in combustion mode, produces an estimated valueof an additional resistive torque as a function of a combination of theobserved value and of the measured value of the output variable.
 6. Thecontrol device according to claim 5, wherein the combination is adifference between the observed and the measured value of the outputvariable.
 7. The control device according to claim 2, wherein the outputvariable is a rotational speed of the engine.
 8. The control deviceaccording to claim 5, wherein said estimator produces an estimated valueof the transmission torque based on the engine speed and the estimatedvalue of the additional resistive torque.
 9. The control deviceaccording to claim 5, wherein said observer supplies an observed valueof the engine output variable which is also a function of the estimatedvalue of the additional resistive torque.
 10. The control deviceaccording to claim 5, wherein the combination is a difference betweenthe observed and the measured value of the output variable.
 11. Thecontrol device according to claim 8, wherein said calculator has aregulator with an input variable being a difference between the datumvalue and the estimated value of the transmission torque.